Effects help to refine or reshape audio signals. Reverb, Delay and Chorus are just a few examples of effects that can be used on audio signals.
Reverb is the persistence of an acoustic signal after the original signal has ceased (similar to an echo). Delay can be explained in 3 stages. (1) The first stage of a five-stage DADSR envelope, which delays the beginning of the envelope's attack segment. (2) A control function that allows one of the elements in a layered sound to start later than another element. (3) A signal processor, used for flanging, doubling, and echo, that holds its input for some period of time before passing it to the output, or the algorithm within a signal processor that creates delay.